Collision sensor for motor vehicle safety device

ABSTRACT

A deceleration-sensitive switch adapted to be closed by movement of a weight at the time of a collision. An electromagnet normally keeps the weight away from the switch to open it. The electromagnet is supplied with a current signal varying in magnitude with vehicle speed, so as to vary the minimum deceleration above which the weight is released from the electromagnet to close the switch. The current signal is obtained through proper processing of a vehicle speed signal proportional to the rotational speed of a vehicle wheel. In order to compensate for the deviation of the detected vehicle speed from the actual value that would occur when the vehicle wheels are suddenly locked by the brackes, the vehicle speed signal is arranged to decrease at a certain rate during a rapid decrease of the wheel&#39;&#39;s rotational speed.

D United States Patent 1 91 1111 3,882,958

Hosaka et al. Ma 13, 1975 [54] COLLISION SENSOR FOR MOTOR 3,650,5753/1972 Okamoto 188/181 C 3,717,731 2/1973 Porter et al. VEHICLE SAFETYDEVCE 3,736,435 5/1973 Runge et al. 303/21 CG [75] Inventors: AkioHosaka; Kosaku Baba, both of Yokohama Japan Primary Examiner-DavidSchonberg [73] Assignee; Nis M t Company Li it d, AssistantExaminer-John P. Silverstrim Yokohma City, Japan 221 Filed: Nov. 21,1972 L 1 ABSTRAET A ece eration-sensitive switc adapted to be closed[2]] 308560 by movement of a weight at the time of a collision. Anelectromagnet normally keeps the weight away from Foreign ApplicationPriority Data the switch to open it. The electromagnet is supplied Feb.1, 1972 Japan 47-12824 with a current Signal varying in magnitude withvehicle speed, so as to vary the minimum deceleration above [52] Cl.180/105 200/6145 M; 303/21 CE which the weight is released from theelectromagnet 51 1111. C1. Br 21/02 0186 the switch- The current Signalis obtained 58 Field of Search 180/103, 10s, 82 R; thmugh P 1 Pmcessingof a vehicle Speed Signal 280/ 303/21 C 21 CE 21 CF; proportional to therotational speed of a vehicle 200 M wheel. In order to compensate forthe deviation of the detected vehicle speed from 'the actual value that[56] References Cited would occur when the vehicle wheels are suddenlylocked by the brackes, the vehicle speed signal is ar- UNITED STATESPATENTS ranged to decrease at a certain rate during a rapid deg -g lcrease of the wheels rotational speed. ass e 3,603,612 9/1971 Hill etal. /105 E 9 Claims, 13 Drawing Figures SPEED 50/ V1 v2 10 DECLN SAFETYSENSOR CONV. MOD, CONT.

I I I SENSOR DEVICE 1 l2 l3 l4 1 6 1 mma HAY 1 31975 3 882 958 SHEEI 10$2 IO F/g. /%fi SPEED SW VI \/2 1C DECLN I SAFETY COI\|\/.-l\/!OD CONT.SENSOR I SENSOR DEVICE (H l2 l5 l4 1 1 COLLISION SENSOR FOR MOTORVEHICLE SAFETY DEVICE This invention relates to motor vehicle safetydevices and, more particularly, to an improved collision sensorincluding a deceleration-sensitive switch whose minimum decelerationrendering the switch closed is varied with vehicle speed so as toprevent undesired actuation of the safety device.

Heretofore, many types of collision sensors have been proposed foractuation of motor vehicle safety devices. In certain of them, adeceleration-sensitive switch is provided which includes a weightadapted to move the switch to a closed position .at the time of acollision. Usually, the weight employed has a relatively small mass sothat in the case of a collision at high speeds it can close the switchwithin approximately ten milliseconds to secure safely protection ofvehicle occupants from injuries. However, there is a tendency forswitches of this type to be closed by a small impact which would resultfrom a slight collision such as one occurring at relatively low vehiclespeed, although, in this case, actuation of the safety device isundesired.

To eliminate this difficulty, it has been proposed that the minimumdeceleration G above which the switch is designed to be closed is variedwith vehicle speed. That is, for lower vehicle speeds, the minimumdeceleration G is increased to prevent undesired actuation of the safetydevice, while, for higher vehicle speeds, the G, is lowered to providefor quick response to a collision condition. As will be appreciated bythose skilled in the art, this scheme of varying the minimumdeceleration G is realized through the provision of a perma- 1 nentmagnet and an electromagnet both acting to normally keep the weight in aposition opening the switch, the electromagnet being supplied with acurrent signal of a magnitude dependent upon vehicle speed from anelectronic circuit for converting the wheels rotational speed into thecurrent signal. However, there exists problem that if a slippage occurrsbetween the tires and the road, the detected vehicle speed tends todeviate from the actual value. Especially, in such a case that thewheels are suddenly locked by the brakes during travelling on a slipperyroad, the detected vehicle speed becomes far lower than the actualvalue. Since, in this condition, the switch is arranged to have a higherminimum deceleration G there is a likelihood that the switch fails toactuate the safety device at the time of a collision.

Therefore, it is an object of the present invention to provide animproved collision sensor for a motor vehicle safety device with a viewof overcoming the abovestated disadvantages.

Another object of the present invention is to provide an improvedcollision sensor whose minimum deceleration rendering the safety deviceactuated is varied with vehicle speed.

It is a further object of the present invention to provide an improvedcollision sensor that insures actuation of the safety device uponsensing of a collision condition even when a slippage of the wheelsoccurs causing a deviation of the detected vehicle speed from the actualvalue.

These and other objects will be readily apparent from the followingdescription of the invention when read in conjunction with theaccompanying drawings, in which:

FIG. 1 is a block diagram of a collision sensor embodying the invention;

FIG. 2 is a circuit diagram of the frequency-voltage conversion circuitof FIG. 1;

FIGS. 3(a) to (d) show the waveforms appearing at various points in thecircuit of FIG. 2;

FIG. 4 is a circuit diagram of the modulator circuit of FIG. 1;

FIGS. 5(a), (b) and (c) show the actual vehicle speed, the input voltageand output voltage of the circuit of FIG. 4, respectively;

FIG. 6 is a circuit diagram of the control circuit of FIG. 1;

FIG. 7 is a modification of the control circuit; and

FIG. 8 is a diagrammatic sectional view of the deceleration sensor ofFIG. 1.

A simplified block diagram illustrating the overall arrangement of thecollision sensor according to the invention is shown in FIG. 1.

The collision sensor includes a vehicle speed detector 10 whichcomprises a speed sensor 11 and a frequencyvoltage conversion circuit12. The speed sensor 11 may be of any conventional type capable ofgenerating an a.c. signal S with a frequency proportional to therotational speed of a vehicle wheel. The frequency-voltage conversioncircuit 12 functions to respond to the a.c. signal 8,, from the sensor11 to generate an analog voltage V that is proportional to therotational speed. The analog signal V is supplied from the conversioncircuit 12 to a modulator circuit 13. The modulator circuit 13, inresponse to the analog signal V generates a vehicle speed signal V whichfollows the V during an increase and slow decrease of V However, whenthe V rapidly decreases at more than a predetermined rate, the V isarranged to decrease at a certain rate of this rate of decrease ismaintained during such decrease of V Thus, if, at sudden braking, thewheels are locked by the brakes causing a rapid decrease in the V the Vexhibits the certain rate of decrease which is arranged to approximatelyequal that decrease of the actual vehicle speed.

Connected to the modulator circuit 13 is a control circuit 14 whichgenerates an current signal I dependent upon the vehicle speed signal Vsupplied from the modulator circuit 13. The current signal I is variedby the control circuit 14 to change with the minimum deceleration abovewhich a safety device 15 is to be actuated, in accordance with vehiclespeed. The control circuit 14 is further connected to a decelerationsensor 16 including a switch (not shown in FIG. 1). The switch isnormally kept in an open position but is immediately rendered closedwhen a collision takes place. The deceleration sensor 16 furtherincludes an electromagnet or a combination of an electromagnet and apermanent magnet (not shown in FIG. 1) for normally maintaining theswitch in the open position. The electromagnet is supplied with thecurrent signal I so as to vary a force exerted on the switch therebychanging the minimum deceleration above which the safety device 15 is tobe actuated. The safety device 15 is connected to the switch of thedeceleration sensor 16 for actuation of a gas bag or other shockabsorbing means comprising the device 15 at the time of a collision.

In FIG. 2, there is shown a typical circuit arrangement of thefrequency-voltage conversion circuit 12 shown in FIG. I. Alphabeticalcharacter a designates an input end of the conversion circuit 12 whichis connected to the speed sensor 11 (shown in FIG. 1) so as to besupplied with the ac. signal S,,. therefrom. The input end a isconnected to a Schmitt trigger circuit 20 of a conventional constructionand comprises transistors Q and Q of the NPN type, resistors R through Rand a capacitor C the collector of the transistor Q2 forming an outputb. As is well known, the Schmitt trigger circuit 20 functions to respondto the a.c. signal S,,., the waveform of which is shown in FIG. 3(a), togenerate a rectangular wave signal having a repetition period t thewaveform of which is also shown in FIG. 3(b). However, if the speedsensor 1 1 is constructed in a way to generate a rectangular wave signalhaving a repetition period dependent upon the rotational speed of avehicle wheel, it will be appreciated that the Schmitt trigger circuit20 may be omitted, of course.

The rectangular waveform output derived from the transistor O issupplied to a monostable multivibrator 22 of a conventional constructionand comprises transistors Q and Q of the NPN type, a diode D resistors Rthrough R and capacitors C and C The monostable multivibrator 22 isconnected to an invertor 24 comprising a transistor Q and resistors Rand R .with the collector of the transistor Q forming an output 0 of theinvertor. The invertor 24 serves to reduce the output impedance of themonostable multivibrator 22. The pulse signal at c, as is shown in FIG.3(0), is of a width t that is dependent upon the values of the resistorR and the capacitor C The pulse signal is further supplied to a filtercircuit 26 comprising a diode D resistors R and R and a capacitor CIndicated at d is the output of the frequency-voltage conversion circuit12 which is connected to the point between the resistor R and thecapacitor C FIG. 3(d) illustrates the waveform appearing at d which isproduced through charging and discharging of the capacitor C Undernormal condition, the fact that the amount of electric charge flowinginto the point d is equal to that flowing therefrom yields the followingequation:

where V represents supply voltage.

This equation is equivalent to:

In the above equation, it is understood that the values of the resistorsR and R and the time t are constant. Thus, the equation can beapproximated by:

13 generally comprises an input impedance converter 39 and aconstant-current discharge circuit 31. The impedance converter 30includes a transistor Q of the PNP type with its emitter connected tothe supply voltage V through a resistor R and with its collectorgrounded. The base of the transistor 0,, forms an input end d of themodulator circuit 13 to which is applied the analog signal Vproportional to the vehicle speed.

The constant-current discharge circuit 31 includes a transistor Q of theNPN type with its collector connected to the emitter of Q through adiode D A capacitor C is provided which connects the collector O to theground. The transistor 0, is connected at its emitter to the groundthrough a resistor R and at its base to the supply voltage and to theground through resistors R and R respectively. The output voltage V ofthe modulator circuit 13 is obtained from a terminal e leading from thecollector of the transistor Q Under a normal condition, the capacitor Cis charged to a level approximately equal to the input voltage V Forexample, when the voltage V increases tp V, along the line 33 shown inFIG. 5(b), a current flows through the resistor R and the diode Dcharging the capacitor C to the same level as V as is seen in FIG. 3(0).In order that the charging voltage appearing at the positive terminal ofthe capacitor C i.e., the output voltage V might follow the inputvoltage V quickly, it is important to employ the resistor R ofrelatively small value to provide a reduced time constant. On the otherhand, as the input voltage V, gradually decreases along the line 35shown in FIG. 5(b), the output voltage V attempts to follow the inputvoltage and drops to the same voltage as V as is seen in FIG. 5(0). Thisvoltage drop is brought about by the discharging of the capacitor Cthrough the constant-current discharge circuit 31. At this time, thediode D functions to prevent flow therethrough of the dischargingcurrent. However, if the input voltage V, rapidly decreases, as shown bythe line 37, the output voltage V cannot follow the input voltage andaccordingly decreases at a certain rate dependent upon thecharacteristics of the constant-current discharge circuit 31. In thepreferred embodiment of the invention, the rate of decrease is selectedto equal the rate of decrease of vehicle speed, i.e., the decelerationwhich is believed to occur when the brakes are suddenly applied duringtravelling on a relatively slippery road. The value of the decelerationlies in the range of 0.1 to 0.3 G (G: gravitational acceleration). Thus,it will be appreciated that the output voltage V increases and decreasesin substantially the same manner as the actual vehicle speed does, aswill be readily apparent from comparison between FIGS. 5(a) and (c).

In FIG. 6, there is shown an example of the control circuit 14 formingpart of the collision sensor according to the present invention. Thecontrol circuit 14 includes a transistor Q of the PNP type with its baseconnected to the terminal e of the modulator circuit 13 shown in FIG. 4.The transistor Q, has its emitter connected to the supply voltage Vthrough a resistor R and its collector connected to a coil 40 whichforms part of the electromagnet included in the deceleration sensor 16(shown in FIG. 8). As will be understood, the current I, flowing fromthe collector of 0,, into the coil 40 is inversely proportional to theinput voltage V A modified form of the control circuit 14 is shown inFIG. 7. Although, in the embodiment of FIG. 6, the

output current I, varies continuously as the input volttermined valuesin accordance with the voltagev The control circuit 14 as shown includesa voltage divider comprising resistors'R' and R which are arranged toprovide a reference voltage V, at the point 50 therebetween.Thereference voltage V, corresponds to a certain vehicle speed which, inthis embodiment, lies in the range of 5 to 30 km/h. The point 50 isconnected to one input terminal of a comparator 51, the other of whichis connected to the terminal e of the modulator circuit '13 so as to besupplied with the vehicle speed signal V therefrom. The comparator 51functions to compare the two voltages V, and V, and to provide an outputsignal when V, is greater than V The output of the comparator 51 isconnected through a resistor 53 to the base of a transistor 0,, of thePNP type, the collector thereof being connected through a resistor R tothe coil 40 of the electromagnet provided in the deceleration sensor 16.Thus, when V, is greater than V the comparator 51 renders the transistorQ conductive, thereby energizing the coil 40. On the other hand, when V,is smaller than V the transistor Q remains non-conductive, causing nooutput current I, to flow through the coil 40.

In FIG. 8, there is shown a typical arrangement of the decelerationsensor 16 according to the invention. The deceleration sensor 16includes a generally cylindrical body 54 of non-magnetic, electricallyinsulating material having a chamber 55. Within the chamber 55 areprovided a contact 57 extending thereinto through the body 54 and aweight 58 of magnetic material, the contact and the weight comprising aswitch for actuating the safety device (shown in FIG. 1). The weight 58is suspended within the chamber 55 by a conductive wire 60 which leadsto a terminal 2'. Another terminal j is provided leading to the contact57.

A permanent magnet 62 and an electromagnet 63 are provided in a body 54to normally keep the weight 58 away from the contact 57. Theelectromagnet 63 includes the coil 40 having one end grounded and theother connected to the control circuit 14.

Let it be assumed that forces F and F are exerted upon the weight 58having a mass m by the permanent magnet 62 and the electromagnet 63,respectively. In this case, it will be appreciated that the weight 58remains in the position shown until the deceleration exceeds F, F /m.When the deceleration sensor 16 is subjected to a deceleration greaterthan F, F /m, the weight 58 moves in a right-hand direction as viewed inFIG. 8, coming into electrical contact with the contact 57, so that thesafety device 15 is actuated.

In this connection, it should be noted that the force F exerted by theelectromagnet 63 is of magnitude dependent upon the current l suppliedfrom the control circuit 14. If the coil 40 is wound in such a mannerthat the F increases as the I, increases, then, since the I, is arrangedto be inversely proportional to the vehicle speed as has been explainedin conjunction with the embodiment of FIG. 6, the value F F /m decreasesas the vehicle speed increases. Where the arrangement of FIG. 7 isemployed, the F F /m is kept at a small value during greater than thecertain vehicle speed determined by the resistors R and R while, on theother hand, the F, F lm is kept at a large value during lower than thecertain vehicle speed. However, if the control circuit 14 is designed toproduce an output curre'nt'l propor'tional to the vehicle speed-signalV,, as

different from the embodiments of FIGS. 6 and 7, then it is necessary tomodify the deceleration sensor 16 so that the direction of the force Fexerted upon the weight 58 by the electromagnet 63 is reversed.

Thus, it will be appreciated that the minimum deceleration above whichthe deceleration-sensitive switch is closed is varied with vehicle speedin a manner to prevent undesired actuation of the safety device.

I What is claimed is:

1. A collision sensor for sensing a collision condition of the motorvehicle to actuate a safety device mounted thereon, said sensorcomprising: I a normally open switch for actuating said safety devicewhen closed, a weight member of magnetic material for moving said switchto a closed position in response to inertial force of decelefation, magnetic means for producing a magnetic biasing force for normally biasingsaid weight member in the normally opened position, and

means for varying said magnetic biasing force according to vehicle speedso that said biasing force is reduced as the vehicle speed increases,said means for varying said magnetic biasing force comprising:

means for generating a first signal of a magnitude proportional to therotational speed of a vehicle wheel;

means for generating a second signal responsive to said first signal,the magnitude of said second signal being arranged to follow that ofsaid first signal during an increase and a slow decrease in magnitude ofsaid first signal but to decrease at a predetermined rate during a rapiddecrease in magnitude of said first signal;

means for generating a third signal of a magnitude controlled by saidsecond signal, said third signal being received by said magnetic means,for varying said magnetic biasing force, whereby said magnetic member ismovable to its switch closing position only at the time the inertialforce is of such magnitude as to overcome the magnetic biasing force.

2. A collision sensor as claimed in claim 1, in which the predeterminedrate of decrease in magnitude of said second signal is arranged to equalthe rate of decrease of the vehicle speed occurring when the vehiclewheels are suddenly locked by the brakes during travelling on a slipperyroad.

3. A collision sensor as claimed in claim 2, in which said rate ofdecrease of the vehicle speed lies in the range of 0.1 to 0.3 G (G:gravitational acceleration).

4. A collision sensor as claimed in claim 1, in which said means forgenerating a second signal comprises an input impedance converter and aconstant-current discharge circuit.

5. A collision sensor as claimed in claim 4, in which said inputimpedance converter includes a transistor of the PNP type with itsemitter connected to the supply voltage through a resistor and with itscollector grounded, the base of said transistor forming an input of saidconverter.

6. A collision sensor as claimed in claim 5, in which saidconstant-current discharge circuit includes a transistor of the NPN typewith its emitter grounded through a resistor and with its base connectedto the supply voltage and to the ground through respective resistors, adiode connected between the emitter of said transistor of the PNP typeand the collector of said transistor of the NPN type in a direction toprevent current flow from the latter to the former, and a capacitorconnected between the collector of said transistor of 8. A collisionsensor as claimed in claim 1, in which said means for generating a thirdsignal comprises a voltage divider comprising two serially connectedresistors, a comparator having two inputs, one of which is connected tothe point between said two resistors, the other of which forming aninput of said means for generating a third signal, and a transistor ofthe PNP type with its base connected to the output of said comparatorthrough a resistor and with its emitter connected to the supply voltage,the collector of said transistor being connected to said magnet means.

9. A collision sensor as claimed in claim 8, in which said two seriallyconnected resistors are arranged to provide at a point therebetween avoltage corresponding to a vehicle speed ranging from 5 to 30 km/h.

1. A collision sensor for sensing a collision condition of the motorvehicle to actuate a safety device mounted thereon, said sensorcomprising: a normally open switch for actuating said safety device whenclosed, a weight member of magnetic material for moving said switch to aclosed position in response to inertial force of deceleration, magneticmeans for producing a magnetic biasing force for normally biasing saidweight member in the normally opened position, and means for varyingsaid magnetic biasing force according to vehicle speed so that saidbiasing force is reduced as the vehicle speed increases, said means forvarying said magnetic biasing force comprising: means for generating afirst signal of a magnitude proportional to the rotational speed of avehicle wheel; means for generating a second signal responsive to saidfirst signal, the magnitude of said second signal being arranged tofollow that of said first signal during an increase and a slow decreasein magnitude of said first signal but to decrease at a predeterminedrate during a rapid decrease in magnitude of said first signal; meansfor generating a third signal of a magnitude controlled by said secondsignal, said third signal being received by said magnetic means, forvarying said magnetic biasing force, whereby said magnetic member ismovable to its switch closing position only at the time the inertialforce is of such magnitude as to overcome the magnetic biasing force. 2.A collision sensor as claimed in claim 1, in which the predeterminedrate of decrease in magnitude of said second signal is arranged to equalthe rate of decrease of the vehicle speed occurring when the vehiclewheels are suddenly locked by the brakes during travelling on a slipperyroad.
 3. A collision sensor as claimed in claim 2, in which said rate ofdecrease of the vehicle speed lies in the range of 0.1 to 0.3 G (G:gravitational acceleration).
 4. A collision sensor as claimed in claim1, in which said means for generating a second signal comprises an inputimpedance converter and a constant-current discharge circuit.
 5. Acollision sensor as claimed in claim 4, in which said input impedanceconverter includes a transistor of the PNP type with its emitterconnected to the supply voltage through a resistor and with itscollector grounded, the base of said transistor forming an input of saidconverter.
 6. A collision sensor as claimed in claim 5, in which saidconstant-current discharge circuit includes a transistor of the NPN typewith its emitter grounded through a resistor and with its base connectedto the supply voltage and to the ground through respective resistors, adiode connected between the emitter of said transistor of the PNP typeand the collector of said transistor of the NPN type in a direction toprevent current flow from the latter to the former, and a capacitorconnected between the collector of said transistor of the NPN type andthe ground, the collector of said transistor of the PNP type and thEground, the collector of said transistor of the NPN type forming anoutput of said discharge circuit.
 7. A collision sensor as claimed inclaim 1, in which said means for generating a third signal comprises atransistor of the PNP type with its emitter connected to the supplyvoltage through a resistor and with its collector connected to saidmagnet means, the base of said transistor forming an input of said meansfor generating a third signal.
 8. A collision sensor as claimed in claim1, in which said means for generating a third signal comprises a voltagedivider comprising two serially connected resistors, a comparator havingtwo inputs, one of which is connected to the point between said tworesistors, the other of which forming an input of said means forgenerating a third signal, and a transistor of the PNP type with itsbase connected to the output of said comparator through a resistor andwith its emitter connected to the supply voltage, the collector of saidtransistor being connected to said magnet means.
 9. A collision sensoras claimed in claim 8, in which said two serially connected resistorsare arranged to provide at a point therebetween a voltage correspondingto a vehicle speed ranging from 5 to 30 km/h.